Nitrided article of manufacture



Patented June 22,

NITRIIIJED ARTICLE OF MANUFACTURE Joseph V. Emmons, Shaker Heights, Ohio, as-

signor to The Cleveland Twist 'Drill Company, Cleveland, Ohio, a corporation of 02110 No Drawing. Application October 26, 193 1,

1 Serial No. 750,136

( I 3 Claims.

This invention relates as indicated to nitrided articles of manufacture and this application is a continuation in part of my co-pending application Serial No. 655,861, filed February 8,1933.

5 It has been known for quite some time that a hard case on a steel article may be secured by heating the metal in an atmosphere of nitrogen, ammonia usually being employed as the means for supplying the nitrogen. (See U. S. Patent No.

1,065,379 to Machlet.) It has been recognized, however, that a steel consisting of a simple alloy of iron and carbon does not absorb nitrogen during the customary nitriding process to an extent sufficient to make it usefulas a body material for the production of articles having a nitrided case.

Dr. Adolph Fry made a very important contribution to this art by his suggestion to add aluminum to the alloy being nitrided in order to materially increase the rate of absorption of the nitrogen, thereby reducing the time required to secure sufficient penetration and further, a nitrided case secured in this manner is harder than a case possible on a simple alloy of iron 5 and carbon. It has also been suggested (see Phillips U. S. Patent No. 1,697,083) to add molybdenum as an alloying element to the article being nitrided in order to make possible the rapid absorption of nitrogen and the production of a satisfactory hard case of adequate depth. The nitrided surface or case formed on alloy steel articles of the type suggested by the prior art is usually satisfactory from the standpoint of its hardness and resistance to abrasion but a principal difiiculty has been encountered with the cracking and chipping of the hard-and brittle nitrided surface layer or case due to the plastic deformation of the supporting steel core or body under working pressures.

The prior art hasbeen primarily concerned with the production of hard nitrided cases upon core materials which were too weak and plastic to withstand the high chip pressures encountered with many cutting tools or the concentrated 4g loads frequently occurring in other forms of wear-resisting articles. This is particularly. true because the temperatures at which the nitriding process is customarily effected (900 F. to 1100 F.) are such as to greatly reduce the hardness and strength and increase the plasticity of the steels customarily employed as core materials if they have been previously hardened. A tool formed with a plastic core. of insufficient hardness and,

strength, even though provided with a satisfactory nitrided case of sufficient hardness and capable of withstanding abrasion will, nevertheless, be useless for heavy duty work where the stresses to which the tool will be subjected are sufficient to deform the core to such an extent 0 that the nitrided case will crack or chip.

, as molybdenum tool steels.

It is a principal object of my invention to provide an article of manufacture such as a tool or the like having a hard and brittle nitrided surface and a supporting body of. great strength and hardness.

It is a further object of my invention to provide a supporting core, underneath the hard surface layerof a nitrided case, of greater resistance to plastic deformation than is possible with the so-called nitriding steels of the prior art. This,v combination of properties makes possible a wearing surface which not only has great hardness and resistance to abrasion but which also has strong and rigid support from its underlying and supporting core. With this stronger support, it is possible for the nitrided case to withstand greater pressures without being cracked and broken than is possible with the nitriding steels of the prior art.

Other objects of my invention will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, said invention, then consists of the means hereinafter fully described and particularly pointed out in the claims.

The following description sets forth in detail certain products exemplifying my invention, such disclosed products constituting, however, but

some of the various applications of the principles ject of this invention to provide an article of manufacture having a nitridedsurface supported by an underlying core of exceptionally strong and hard steel capable of withstanding extreme /operating stress without such plastic deformation as will cause a cracking or failure otherwise of the hard nitrided case.

The alloy steel compositions suitable for body material for nitrided articles in accordance with the present invention are characterized by a relatively high molybdenum content. The alloy steel compositions hereinafter referred to are all of such character that they may be properly defined The following table sets forth the broad ranges of percentages within which the several alloying elements may be present:-

Percent Carbon 0.25 to 1.30 Manganese None to 2.00 Silicon None to 3.00 Chromium None to 15.00 Tungsten None to 6.00 Vanadium None to 5.00 Molybdenum 4.00 to 15.00

alloy steels. v i A still-further example-.01 a specific alloy steel composition successfully utilized for A somewhat narrower range of percentages within whichthe several alloying elements may be present is as follows:

- -Per cent Carbon, 0.50 to, 1.00 Manganese Noneto 2.00 Silicon" Noneto 3.00 Chromium None to 5.00 Tungsten None 1:04.00 Vanadium None to 3.00 Molybdenum 6.00 to 12.00

the remainder being substantially iron together with such other alloying elements and impurities as are sometimes found in alloy steels. In the foregoing tables giving ranges of percentages for theseveral alloying elements, the

lower limits for manganese, silicon, chromium, vanadium and tungsten have been given as none". As previously indicated, this invention relates to molybdenum toolsteels. The tables of percentages previously given are to be interpreted, therefore, as covering only those steels in which the elements manganese, silicon, chromium, vanadium and tungsten are present in a total amount not less than 3.00%, although any one or more of such elements may be entirely absent.

An illustrative specific alloy steel composition which is suitable for body material for nitrided articles is as follows:

the balance being iron, together with such impurities as are usual in alloy steels.

This s'teel possesses properties which approach those .of high speed steel, aithough-the amount of alloy present is much less. than is usually employed in such steels. With this composition a hardening temperature as high as 2200" F. may be employed together with drawing temperatures up to 1150 F. Tools made from this steel such as twist drills, possess great strength and cutting quality, these properties beingmaintained at operating temperatures up to red heat.

After hardening at 2200 F. and nitriding, a steel according to the last above enumerated composition has a. surface layer of great hardness supported by a rigid core of great strength and of a hardness sufhcient to itself function as a cutting tool.

Still another example of a specific alloy steel composition which is suitable for body material for nitrided articles is as follows:

- Per cent Carbon about I 0.66 Chromium do 4.26 Tungsten do 0.10 Vanadium do 1.14 Molybdenum ....do 10.19

the balance being iron, together with such other alloying elements and impurities as are usualin ofthe inventienis as follows 1 steels.

' pering.

the purposes Per cent Carbon -about 0.77 Chromium do- 3.85 Tungsten do 1.90 Vanadium do..- 1.03 Molybdenum do 11.15 Cobalt do 9.06

the balance being iron and such other alloying elements and impurities as are usual in alloy The steel of the last above mentioned composition is of the type in which molybdenum is the principal alloying constituent and contains about one iourth as much tungsten as molybdenum. It also contains a. considerable percentage of cobalt. The body of this steel underneath the nitrided case has exceptional hardness and strength due .to its great resistance to temstill predominantly ma'tensitic.

Another example of a specific alloy steel composition is as follows:-

. Per cent Carbon about 0.87 Manganese do 0.12 Silicon do 0.40 Chromium do 3.35 Vanadiumu do 1.31 Molybdenum do 7.65 Nickel do 2.17

Its microstructure, after nitriding, isv

the balance being iron together with such other alloying elements and impurities as are usual in alloy steels.

This steel is notable for a substantial nickel content. It has an unusal resistance to tempering, maintaining a high hardness after tempering treatmentswhich approach tool steel annealing conditions. It takes a nitrided case of great hardness and depth. Y

Another example of a specific alloy steel composition is as follows:-

Per cent Carbon 1.29 Manganese 0.11 Silicon -l 0.47 Chromium 3.29 Tungsten 1.61 Vanadium 3.29 Molybdenum 8.04

strength.

The compositions hereinbefore enumerated are sufliciently hard and of such great strength so thatwhen tools and like articles made therefrom are subjected to severe working stresses the supporting core for the nitrided f case will not be deformed and the case will accordingly be preserved against cracking andchipping.

The utility of such nitrided cases is'not confined to the cutting portion'of tools but may be widely extended to suchpurposes as pilots, guides,

20 given specification.

or other articles and parts which are subject to abrasion or wear.

As an example, nitrided parts so supported may be used in complex tools of which the principal cutting or wear-resisting action is perany specification, for a particular alloy composition must permit of certain variations due to the fact that in making up the composition, it is extremely difdcult, if not impossible, to commercially produce a composition exactly like a It is to be understood, therefore, that throughout the description and claims where I have used figures to denote definite amounts and ranges, such amounts and ranges are to be construed to include the range of variations usually permissible in-maklng up alloy compositions to given specifications. I

Other forms may be employed embodying the features of my invention instead of the one here explained, change being made-in the form or construction, provided the elements stated by any of the following claims or the equivalent of such stated elements be employed.

1, therefore, particularly point out and distinctly claim as my invention:

1. The method of producing a metallic article such as a. tool, having great body strength and a hard wear-resistant surface, which comprises forming the body! of such article of a ferrous alloy characterized by the presence therein of:

Carbon. from about 0.25% to about 1.30%

45 in amounts not exceeding the following percentages: I

- Per cent Manganese 2.00

Silicon 3.00

n Chromium 15.00

Tungsten 6.00

Vanadium 3.00

Molybdenum from about 4.00% to about 15.00%

and a total of not less than 3% of at least one of the following elements individually present hardening said body by heat treatment, and by subsequent heat treatment tempering the'core I and nitriding the surface of said body, an effect of the presence of the named alloying elements in said body being to prevent the decomposition during said tempering and nitriding of a substantial portion of the martensitic structure of said May.

- 2. The method of producing a metallic article such as a tool, having great body strength and ahard wear-resistant'surface, which comprises forming the body of such article of a ferrous alloy characterized by the presence therein of the following elements within the percentages given:

, Per cent Carbon from about 0.50% to about s 1.00 Molybdenum from about6.00% to about 12.00

Manganeseufrom an effective amount to Y 2.00 Silicon from an effective amount to 3.00 Chromium from an effective amount to 5.00

Tungstcn from an effective amount to 4.00 Vanadium from an eii'ective amount to 3.00

a hard wear-resistant surface, which comprises forming the body of such article of a ferrous alloy characterized by the presence therein of the following elements within the percentages given:

Per cent Carbon about 0.77 Chrom do 3.85 Tungsten do 1.99 Molybdenum -do 11.15 Vanadium do 1.03 Coba do 9.06

hardening said body by heat treatment, and by subsequent heat treatment tempering the core and nitriding the surface of said body, an effect of the presence of the named alloying elements in said body being to prevent the decomposition during said tempering and nitriding of a substantial portion of the martensitic structure of said body.

. JOSEPH V. EMMONS. 

